In the not-to-distant past, there was little or no consideration given to the reclamation of refrigerant. Because of environmental ignorance and low costs, when a refrigeration system (e.g., refrigeration or freezer units, air conditioning units, etc.) would break down or when the refrigerant in such system would become contaminated to the point that the effectiveness of the refrigeration system was compromised, the refrigerant would simply be vented into the atmosphere.
Recent developments based on environmental concerns have greatly effected how refrigerant must be handled. In many areas throughout the world it is now illegal to vent refrigerants to the atmosphere--in almost any quantity. In addition, and not coincidentally, the price of refrigerants has also risen dramatically. There is now a significant demand for refrigerant reclaim systems capable of drawing refrigerant from a refrigeration system, cleaning and storing said refrigerant for reuse. Systems that can perform this function 1) efficiently, 2) with little or no mechanical failures, and 3) on all commercially utilized refrigerants (and those new refrigerants that are being and will be developed in the future) will find an enormous market.
One of the major obstacles in this field, is that there are already a variety of refrigerants commonly in use. The type of refrigerant utilized for a particular application is based generally on the load requirements and temperature ranges required. Each of the refrigerants utilized (e.g., those commonly referred to as R-12, R-500, R-11, R-22, R-502) have different boiling points and heats of vaporization, and the design of a single reclaim that will accommodate all of these refrigerants has been elusive. In particular, new cost-effective reclaim systems capable of working with R-11--refrigerant used in many large commercial air conditioning and refrigeration systems--are highly desireable.
Although a wide variety of reclaim designs exist, most refrigerant reclaims fit within one of two general types of systems. In the first type of reclaim, the driving force for drawing the refrigerant from the refrigeration system is a refrigerant compressor. Because effective refrigerant reclaims must be capable of evacuating both liquid and gaseous refrigerant, these reclaims must first assure that the refrigerant is completely vaporized before it enters the compressor. The refrigerant then needs to be condensed for storage. At some point, the refrigerant is passed through some purification element.
U.S. Pat. No. 4,967,570 of Van Steenburgh, Jr. (the inventor of the present application) is illustrative of this type of reclaim. A heat exchange element is used to make the vaporization and condensation steps of the process more efficient. After vaporization of the incoming refrigerant, the gaseous refrigerant is passed through a gradient velocity oil separation chamber before entering the compressor. After condensation, the liquified refrigerant is introduced into a storage chamber. To provide additional purification of the refrigerant, the refrigerant in the storage cylinder is recirculated as part of a refrigeration cycle to lower the temperature of the reclaimed refrigerant and maximize the removal of impurities.
U.S. Pat. No. 4,998,416 of Van Steenburgh, Jr. describes a number of improvements to the basic design of the system described in the U.S. Pat. No. 4,967,570, and points out some of the frailties of a reclaim design that uses an in-line compressor. For example, probably the biggest problem is in the significant load variations that are demanded of a compressor in a reclaim system. The mass flow of refrigerant through the compressor varies by orders of magnitude when liquid refrigerant is being reclaimed compared to when gaseous refrigerant is entering the system. The U.S. Pat. No. 4,998,416 describes the use of means for cooling the compressor motor windings when the load requirements on the reclaim are reduced. This mechanism eliminates compressor failures caused by overheating and load variations.
Because the reclaim described in U.S. Pat. No. 4,967,570 and U.S. Pat. No. 4,998,416 contains an expansion/recycling refrigeration cycle, it is also necessary to include a plurality of expansion valves to allow for the use of the same reclaim with a number of refrigerants.
The U.S. Pat. No. 4,998,416 describes one of the most efficient and trouble-free refrigerant reclaims available to date. However, even the apparatus disclosed therein is not capable of reclaiming all refrigerants. In particular, R-11 refrigerant can not be utilized with conventional, relatively small refrigerant compressors. Due to the physical characteristics of this widely used refrigerant, it is virtually impossible to maintain adequate oil lubrication within such compressors, and compressor destruction is the inevitable result.
As mentioned above, there are two general types of refrigerant reclaim systems. In the second type, the driving force for drawing the refrigerant from the refrigeration system is the reduction in pressure at a point downstream within the refrigerant reclaim. The low pressure regime is created by reduced temperature induced by a separate refrigeration cycle. In most of these systems, the refrigerant within the separate refrigeration cycle is the same refrigerant that is being reclaimed. See, e.g., U.S. Pat. No. 4,766,733 of Scuderi; U.S. Pat. No. 4,809,515 of Houwink, U.S. Pat. No. 4,903,499 of Merritt; and U.S. Pat. No. 4,939,903 of Goddard. These are really hybrid systems since both the reduced temperature and the compressor are used to withdraw the refrigerant into the reclaim.
An apparatus analogous to the second type of reclaim is described in U.S. Pat. No. 4,539,817 of Staggs et al. In Staggs, a completely separate refrigeration system is used to drive the withdrawal of refrigerant. Staggs, however, is simply a recovery and charging device. Staggs does illustrate how it would be possible to withdraw refrigerant from a refrigeration system without having to pass the refrigerant being reclaimed through a compressor.
The recovery and charging system disclosed in the Staggs patent has several major deficiencies. As in the type of reclaims that utilize compressors, the effects of widely varying loads is not addressed in Staggs. Even though a separate refrigeration cycle drives the withdrawal of refrigerant in Staggs, there are still dramatic load differentials on the compressor of the independent refrigeration system.
When the load requirements on a refrigeration cycle vary dramatically, the loss of load results in the loss of a mechanism for restoring heat to the refrigerant in the evaporator section of the refrigeration cycle. To compensate for this loss, liquid refrigerant may not be vaporized by the expansion valve, and some liquid refrigerant enters the compressor. This condition leads quickly to compressor destruction by "liquid slugging."
In Staggs, the heat exchange coil of the independent refrigeration cycle is contained within the refrigerant storage cylinder. By choosing the direction of flow of the independent refrigeration cycle, the heat exchange coil can act to either reduce the temperature of the interior of the chamber (thus drawing refrigerant to it) or raise the temperature of the interior of the chamber (thus aiding in the discharge of refrigerant). Although the theory of operation for such an apparatus is straightforward, by restricting the location of the heat exchange coil to the interior of the chamber it is generally impossible to maximize the temperature reduction--and pressure reduction--to allow the refrigerant withdrawal to proceed within commercially reasonable time frames. The same is also true for raising the temperature to discharge refrigerant from the storage cylinder.
It was the goal of the present invention to develop a refrigerant reclaim system that is capable of efficiently reclaiming all refrigerants in a single apparatus. By removing the in-line compressor as utilized in the U.S. Pat. No. 4,967,570 and U.S. Pat. No. 4,998,416, it was possible to accommodate all refrigerants. However, the system also had to include means for purifying the reclaimed refrigerant, means for making the reclaim operate as efficiently as those using in-line compressors, and means for preventing compressor destruction due to liquid slugging.